1. Technical Field
The technical field relates to a defective pixel detecting device for detecting defective pixels of a solid-state imaging device, a defective pixel detecting method, a recording medium storing a program for detecting defective pixels, and an imaging apparatus.
2. Related Art
Solid-state imaging devices such as CCDs made of semiconductor often include defective pixels due to local crystal defects in the semiconductor. It is known that image degradation due to imaging output of such defective pixels, or so-called white spots or black spots, may occur in an image taken by a solid-state imaging device including the defective pixels.
Accordingly, in the recent years, a defect detecting and correcting system has been proposed that detects and corrects defective pixels with a solid-state imaging device being set in a video camera and such. With this type of defect detecting and correcting systems, when scanning and detecting within a one screen, defective pixels are sequentially detected from an edge of the screen, and defection data as information relating to the detected defective pixels is sequentially stored in a memory. The defection data stored when each defective pixel is detected includes address data that specifies an absolute position of the defective pixel on the screen and/or a defection level as a video signal level of the defective pixel.
When actually mounting such a defect detecting and correcting system in a device such as a video camera, an amount of defection data that can be stored is limited by a storage capacity of a memory mounted in the device.
According to this defect detecting and correcting system, a checkup for defective pixel detection is sequentially carried out from a first line within a screen, and defection data for the detected defective pixels is stored in a memory in real time when defective pixels are detected, thereby completing the scanning of a single frame. Therefore, when a number of the defective pixels that are present is over the storage capacity of the memory, defection data for defective pixels that are detected after the number of detected defective pixels exceeds the memory capacity cannot be stored in the memory. Thus, a problem has been noted that defects are corrected only for a first half of the screen, for example.
Thus, a technique for detecting and correcting defective pixels over an entire screen by effectively using a memory with a limited storage capacity, for example, are disclosed in Patent Documents 1 to 3.
According to a conventional defect detecting and correcting system disclosed in JP-A-06-315112 (Patent Documents 1), when detecting defective pixels by comparing an imaging output level of a solid-state imaging device with a predetermined threshold value (detection level), re-detection is carried out with lowered detection sensitivity by increasing the predetermined detection level if a number of the detected defective pixels exceeds an allowable number for storage corresponding to the storage capacity of the memory. The re-detection is repeated until the number of defective pixels becomes equal to or smaller than the allowable number for storage. With this, the detection and correction of the defective pixels over an entire screen can be carried out by effectively using a memory with a limited storage capacity.
Further, according to a conventional defect detecting and correcting system disclosed in JP-A-07-59011 (Patent Documents 2), defective pixels are detected and the defective pixels of an allowable number for storage corresponding to the storage capacity of a memory are stored, and then, defection levels of the detected defective pixels are compared with defection levels of the defective pixels stored in the memory. If it is determined that the defection level of a detected defective pixel is greater than the defection level of a stored defective pixel, the defective pixel with a smaller defection level is replaced with the defective pixel with a greater defection level and stored in the memory. With this, the defective pixels are detected and corrected from the pixel with a higher defection level until the number of defective pixels reaches the allowable number for storage corresponding to the storage capacity of the memory.
Moreover, according to a conventional defect detecting system disclosed in JP-A-2005-123873 (Patent Documents 3), a different detecting method is disclosed as follows in addition to the method according to JP-A-07-59011 described above. That is, this detecting method is configured to store detection time(date) as attribute information of defective pixels in place of the defection levels. Specifically, after the defective pixels are detected and the defective pixels of allowable number for storage corresponding to the storage capacity of the memory are stored, defective pixels that are detected currently are stored in the memory in place of defective pixels whose detection time(date) are older.
Furthermore, according to a conventional defect detecting system disclosed in JP-A-2005-123873, both of the defection level and the detection time can be stored as attribute information of defective pixels, and the sorting as described above can be carried out based on one of the defection level and the detection time.
However, according to the above described conventional configurations, it is possible to carry out defective pixel correction by selecting a pixel with higher priority from the pixels that have been detected during the defective pixel detection, but there is a problem that no countermeasure is taken in a case when a pixel that should be normally corrected cannot be detected. Further, defective pixel has a property of changing the signal level according to temperature and charge accumulation time. If the defection level of a defective pixel is accidentally low during the defective pixel detection, such a defective pixel cannot be detected, and accordingly possibly remains uncorrected.